The purpose of this proposal is to gain an understanding of the factors which regulate sequential functions of RNA polymerase in a developmental system. The sporulating bacterium, Bacillus subtilis, will be used as a model system for this investigation. Conditional temperature-sensitive RNA polymerase mutants will be selected which can grow but not sporulate at the non-permissive temperature. These mutants will be selected initially for rifampicin resistance and then for temperature sensitivity during sporulation. These mutants will be grouped according to their morphological block in the sporulation sequence. These stages should indicate putative RNA polymerase modifications or interactions which are altered in these mutants and which leads to their temperature sensitivity. The subunits of the RNA polymerase core from these mutants will be analyzed and compared with the subunits from the wild type. Various fractions obtained during purification of the core will also be tested for their interaction with the mutant and wild type cores. These studies should decide the time and type of RNA polymerase modifications which occur during sporulation and should lead to better understanding of the the role of RNA polymerase in the regulation of genetic transcription during differentiation.